Friday, December 21, 2007

My New Year's Wish List...

- USGS merges all of these different versions of MODFLOW (and various package mismatches) into one universal version (not holding breath on this one)

- New version of SEAWAT2000 with heat transport

- New MODFLOW package for conduit flow (karst)

Rumor has it the last 2 might happen soon.

Happy New Year!

Jim Rumbaugh
Environmental Simulations, Inc.

Groundwater Vistas 5.09 Build 18

One last update before Christmas...

Vistas was not writing a MODFLOW2000 LPF input file correctly if you had all of the following:
- resaturation active
- more than one unconfined layer
- writing Kx values to external files for use with pilot points in Pest

You would know if you hit this one as MODFLOW would not even run.

Wednesday, December 19, 2007

MODFLOW Versions and Storage Coefficient

I have had several emails lately regarding storage coefficients (storage, specific storage, and specific yield) in MODFLOW96, MODFLOW2000, and MODFLOW2005. I thought it was enough to be worth a quick blog...

MODFLOW96 and MODFLOW88 determine which storage coefficient to use based on layer type and comparing the head to the Top of the layer. For layer type 0 (confined), it always uses the storage coefficinet (S). For layer type 1 (unconfined in layer 1), it always uses specific yield (Sy). For layer types 2 and 3, if the head in a cell is above the top of the layer, then it uses S. If the head is below the top of the layer, it uses Sy. This is done on a cell-by-cell basis so that parts of the layer can be confined (S) and part unconfined (Sy).

MODFLOW2000 and MODFLOW2005 only have confined and unconfined layers, like type 0 and type 3 in MODFLOW96 but the principal is the same. However, these MODFLOW versions require you to enter specific storage (Ss). The storage coefficient in a confined layer is then computed for each cell by multiplying Ss by the layer thickness.

Groundwater Vistas does not compute Ss for you if you have S in the storage database. You need to enter the proper values based on the version of MODFLOW you are using. GV will, however, convert from Ss to S for MODFLOW96/88. There is a check-box under Model/MODFLOW/Package Options - BCF tab, that says the storage database contains specific storage (Ss). In this case, GV will multiply Ss by layer thickness for MODFLOW96 and MODFLOW88 BCF Package input.

Clear as mud?

Happy Holidays & Vistas 5.09 Builds 16 to 17

As you can see, not as many changes over the holidays...

- We added a new import for the Lake Package. This is for a delimited text file containing columns of data under Model/MODFLOW2000/Import Lake Transient Data. The file contains transient data for a single lake. The columns in the file must contain a stress period number and at least one of the following: precipitation, evaporation, withdrawal, runoff. You must also have Vistas set up to use the Lake spreadsheets for data entry. See Model/MODFLOW2000/Options - Lake3 tab.

- A bug was found where Vistas was not generating a proper Pest control file when estimating leakance in zones. This was probably broken during changes made for pilot points and since this type of estimation is rare, it was just recently caught.

- A change was made to allow constant concentration cells with zero concentration value for MODFLOW-SURFACT. Before this change, constant concentration cells with concentration specified at zero were ignored.

Thursday, December 06, 2007

Groundwater Vistas 5.09 Build 12 to 15

A lot of the problems we fixed this week are related to importing existing MODFLOW2000/2005 models. Vistas is really good at this if the files were created by another preprocessor. However, when you get models (typically from the USGS) that were created in text editors, GIS, special programs, or some combination, then there can be problems and we had a bunch of them lately.

- When the GMG solver first came out, there was a memory leak. We reported this to the USGS and they fixed it. But they fixed it in a different way than we did and so there were 2 pieces of code releasing the same block of memory. This did not hurt anything until you tried to make two model runs back-to-back.

- Obscure error when importing a MODFLOW2000 well package that has a non-parameter well and a parameter well in the same cell.

- Another obscure error where boundary condition parameters had different cases in parameter names between the definition of the parameter and the usage of the parameter

... by the way ... When I say "obscure", it means that you are very unlikely to run into it, but some unlucky user did run into it!

- MODFLOW2005 also has the new "highest active layer" option for ET. We had it set for MODFLOW2000 but not MODFLOW2005.

- We recently added the FHB Package to Vistas (not to be confused with the HFB Package). Importing an existing FHB Package input file worked with flux boundaries but there was an error for head boundaries

- When importing an existing Lak3 Package input file for a one-stress period model, the lake precipitation and evaporation values were not being saved properly.

- There was a problem creating the file pestgv.bat for PEST runs using MODFLOW-SURFACT when writing Kz to the BCF input file (instead of leakance) and when the option to maintain vertical anisotropy was also on.

- GV was not correctly recognizing well reach numbers for selecting the decision variables in MODFLOW2000-GWM.